The Clean Air Act mandates pollution standards for wood burning fireplaces and stoves. The Environmental Protection Agency (EPA) has set stringent standards with regard to the grams of particulate emissions per hour for non-catalytic stoves. These particulate emissions are substances that are discharged into the air due to the incomplete combustion of fuel. The EPA standards require that a fireplace or stove burn cleanly at all settings or burn rates. Burn rates are measured as the speed in which fuel is consumed by fire. In order to be EPA certified a fireplace must be tested at four different burn rates: low, medium-low, medium-high, and high. The procedures for testing the burn rate of a fireplace or stove typically vary with the size of its combustion chamber.
In addition to these stringent standards, state and local codes have become, even tighter and more rigorous standards than the federal law. For example, the State of Washington has more stringent regulations than is required by the EPA. Further, many cities and local communities have promulgated standards that cannot be met by all existing wood burning fireplaces and most wood burning stoves. New fireplaces or stoves that are not certified to meet these requirements cannot be sold in the United States.
The purpose for these federal, state, and local requirements is to create a clean burning fireplace, which releases a low amount of materials into the atmosphere during combustion. Two methods for providing a clean burning fireplace are shown and described in our U.S. Pat. Nos. 4,766,876 and 5,263,471, incorporated herein by reference. In these patents, fireplaces are described that allow for secondary combustion in the top of the combustion chamber. This secondary combustion provides a more efficient and cleaner burning fireplace. However, there are some limitations to the current fireplace's ability to reduce emissions.
First, it can be difficult to meet the EPA's and other governmental requirements for each of the burn rates even when utilizing secondary combustion as described in U.S. Pat. Nos. 4,766,876 and 5,263,471, which are incorporated herein by reference. This is particularly true for testing larger volume wood burning units tested at a low burn because it is often difficult to create enough heat to ensure sufficient secondary combustion. Typically, the volume of wood burning units is limited to about 3 cubic feet. Second, these fireplaces do not provide stepwise control of the amount of combustion air entering the wood burning during a burn to correspond to a change in a solid fuel. For example, the amount of air needed for combustion may vary for fuels that are changing from an organic state to a charcoal state. Third, these fireplaces may not provide the proper amount of primary air for primary combustion and secondary air for secondary combustion to meet governmental testing standards.
Accordingly, it is desirable to provide a fireplace assembly with an improved ability to meet governmental emission requirements under designated burning conditions.